1. Field of the Invention
The present invention relates generally to digital compositing, i.e., the layering or putting together of images in a digital video domain. More particularly, it relates to a system and method for digital image compositing which gives the user an increased flexibility for such compositing. The invention further relates to a user interface that enables the user to take advantage of the increased flexibility more conveniently,
2. Description of the Prior Art
A variety of systems are known in the art for combining separate video images using a key to provide a foreground image superimposed on a background. For example, such systems are disclosed in Greenburg, U.S. Pat. No. 4,357,624 and Kellar et al., U.S. Pat. No. 4,602,286. It is further known to carry out various forms of soft edge keying to provide a realistic transition between the foreground image and the background image. One form of soft edge keying is disclosed in the Kellar et al. patent, and in Bennett et al., U.S. Pat. No. 4,463,373. Other forms of soft edge keying are disclosed in the following issued U.K patents and published U.K. patent applications: 1,178,330; 1,226,559; 1,570,773; 2,032,217; 2,092,346 and 2,109,193. In particular, one technique for soft edge keying that has particular utility is the use of sub-pixel interpolation, as disclosed in published European application 0 360 559.
Other techniques disclosed in the prior art that are useful in digital video image compositing include clock rate doubling and adaptive decimation, as disclosed in published European application 0 360 557, the use of modified keying signals to adjust boundaries between overlaid images, as disclosed in published European application 0 360 560, and the use of dynamic rounding, as disclosed in Owen, D. P., "Dynamic Rounding in Digital Video Processing," SMPTE Journal, June 1989, pp. 447-450.
Various forms of control interfaces for video signal processing equipment are also known in the art. For example, such interfaces are disclosed in U.S. Pat. Nos. 4,538,188; 4,763,186; 4,857,994 and 4,954,883.
While the art pertaining to digital video image compositing is thus a well-developed one, a need still remains for further improvement in such systems in order to provide improved composite images and to make such equipment easier to operate.